1. Field of the Invention
The present invention relates to an X-ray diagnostic apparatus and X-ray diagnostic method, and more particularly to rotation correction of observed images and display control of an X-ray beam limiting device in an X-ray diagnostic apparatus in which an X-ray generator and so on are carried on a triaxially controlled support unit.
2. Description of the Related Art
In an X-ray diagnostic apparatus, a triaxially controlled support unit is known which carries an X-ray generator for irradiating an object under examination with X-rays, an image intensifier disposed opposite the X-ray generator for detecting X-rays transmitted through the object to provide an optical image, and a TV camera for converting the optical image into a video signal to provide an X-ray image of the object. The X-ray generator, the image intensifier and the TV camera are adapted to rotate on three axes which are orthogonal to one another while keeping their relative position.
FIG. 1 is a schematic illustration of this triaxially controlled support unit.
In this figure, the support unit 40 carries an X-ray generator 10, an image intensifier 20 which are opposed to each other with an object under examination 15 interposed therebetween, and a TV camera 30 connected to the image intensifier 20 and rotates on three mutually orthogonal axes intersecting at the arm center O. In addition to the support unit 40, FIG. 1 shows, in block form, signal processing circuitry for processing a video signal output from the TV camera 30. The video signal is converted to a digital signal by an analog-to-digital (A/D) converter 32, then subjected to imaging processing in an image processing unit 34, converted to an analog signal in a digital-to-analog (D/A) converter 36, and visually displayed on a display unit 38. A rotation correction unit 48 corrects the rotation of the arm, etc., which will be described later in detail.
The first rotation axis is perpendicular to the plane including the arm 42 and passes through the arm center O. Sliding the arm 42 relative to an arm column 44 causes the support unit 40 to rotate around the first rotation axis in the direction indicated by an arrow .alpha.. Hereinafter, this angle of rotation is referred to as an arm slide angle, which is indicated by .alpha.. The second rotation axis corresponds to the arm column 44 itself that rotates in the direction of an arrow .beta.. The angle of rotation of the second axis is referred to as an arm rotating angle, which is indicated by .beta.. The third rotation axis corresponds to the column 46 of the main body of the support unit, which rotates in the direction of an arrow .gamma.. The angle of rotation of the third axis is referred to as an column rotating angle, which is indicated by .gamma..
An X-ray image of the object under examination 15 obtained when the triaxially controlled support unit 40 is set in the reference position is called a "vertical image". The angles of each rotation axis at that point are defined as 0.degree. (i.e., .alpha.=.beta.=.gamma.=0.degree.).
When the support unit 40 revolves on each of the three axes through an angle, the rotation correcting unit 48 rotates the TV camera 30 (more accurately, its head) so that a vertical image can be obtained. For example, when the arm 42 is shifted from the head side of the object under examination 15 or from the side of the object for X-ray photography, the TV camera 30 is controlled to rotate through an angle .phi. equal to an column rotating angle .gamma. so that resulting X-ray images of the object are directed in the same direction, that is, vertical images of the object can be obtained.
In the prior art, the column rotating angle .gamma. is considered, but the two other angles associated with the support unit, i.e., the arm slide angle .alpha. and the arm rotating angle .beta., are not taken into consideration in rotation correction. For this reason, vertical images can be obtained when only the column 46 is rotated. However, when other columns than the column 46 are rotated, correction of an image cannot be made for that rotation. Thus, there arises the possibility that no vertical images may be obtained. That is, when the two other axes are rotated with the column rotating angle .gamma. set at any value, no vertical images can be obtained even if the TV camera 30 is rotated for correction. Thus, even if a comparison is made between a past reference X-ray image and a current X-ray image which have been captured at the same clinical angle, they will look rotated with respect to each other, which involves difficulties in making comparative diagnosis.
Even when the above problems are solved, since the image rotation correction is made only by rotating the TV camera, a problem will arise in that the direction in which an X-ray beam limiting device (including a compensation filter) displayed on the display unit opens or closes and the direction in which the X-ray beam limiting device opens or closes as instructed by a movement operation switch may not coincide with each other. This problem will be described in detail with reference to FIGS. 2A, 2B and 2C.
FIGS. 2A, 2B and 2C show an image 15' of an object and an image 12' of the X-ray beam limiting device displayed on the display unit 38, which are obtained as a result of the conventional image rotation correction method . More specifically, FIG. 2A shows images obtained prior to rotation of the support unit (that is, when the support unit is placed in the reference position), FIG. 2B shows images obtained after the rotation of the support unit but before rotation correction, and FIG. 2C shows images after the images of FIG. 2B have been subjected to rotation correction. In the figures, arrows A1, A2 and A3, which are displayed on the display unit 38, indicate the direction of movement of the X-ray beam limiting device when it is instructed to close in the left/right direction by the X-ray beam limiting device movement operation switch provided on an operating console not shown.
In the case of FIG. 2A where the support unit is set in the reference position, the image 15' of the object is displayed vertically and the image 12' of the X-ray beam limiting device is displayed on the right and left sides of the display unit 38. A 90.degree. rotation of the support unit results in the images shown in FIG. 2B. In this case, the image 15' of the object is displayed rotated (tilted) through 90.degree., whereas the image 12' of the X-ray beam limiting device is displayed on the right and left sides of the display unit as in the case of FIG. 2A because the relative position of the X-ray beam limiting device and the TV camera remains unchanged. Thus, since the image 12' of the X-ray beam limiting device moves to close in the left/right direction as shown by the arrows A2 when an operation to close in the left/right direction is given by the operation switch, the direction in which the image 12' of the X-ray beam limiting device opens or closes coincides with the direction specified by the operation switch 52.
In the conventional X-ray diagnostic apparatus, in order to display the image 15' of the object as a vertical image, the TV camera is rotated through a predetermined angle with the rotation of the support unit to thereby make rotation correction on the image 15' of the object. The resulting image is shown in FIG. 2C. Though the image 15' of the object is displayed vertically, the image 12' of the X-ray beam limiting device is displayed rotated through 90.degree. because the TV camera is rotated through 90.degree. for correction. That is, the image 12' is displayed up and down. If, in the case of FIG. 2C, the operation switch is operated so as to close the X-ray beam limiting device in the right/left direction, then the image 12' of the X-ray beam limiting device will move up and down on the display unit as indicated by the arrows A3 because the TV camera is rotated through 90.degree. with respect to the X-ray beam limiting device.
In the conventional triaxial-holding-device-based X-ray diagnostic apparatus in which the direction of movement of the X-ray beam limiting device instructed by the movement operation switch does not coincide with the direction in which the X-ray beam limiting device image on the display unit moves to open or close, therefore, problems arises in the case of image rotation correction in that maloperation may be caused and operation is troublesome.
As described above, the conventional support unit has the following problems.
(1) No match is found between a reference image obtained in the past at a given column rotating angle and an X-ray image being currently observed at the same column rotating angle, which makes comparative diagnosis difficult.
(2) The direction in which the X-ray beam limiting device displayed on the display unit moves to open or close does not coincide with the direction of movement of the X-ray beam limiting device instructed by the movement operation switch, which may cause maloperation and makes operation troublesome.